1. Field
The following description relates to a three-dimensional holographic image display device.
2. Description of the Related Art
Three-dimensional image display devices that provide a more realistic and effective display of an image are desired in various fields, such as medical imaging, games, advertisements, education, and the military. Accordingly, as a method of displaying a three-dimensional image, a holographic method and a stereoscopic method have been studied.
According to a holography method, an interference signal obtained by overlapping a light from an object and a coherent reference light is recorded and reproduced. The holography method provides certain advantages for realizing a three-dimensional image. For example, the holography method has the merit of depth cue, as compared to the stereoscopic method. The stereoscopic method only depends on a binocular depth cue, such as binocular disparity or binocular convergence, but does not provide a monocular depth cue, such as accommodation. A lack of a monocular depth cue may result in disharmony with a depth cue generated by binocular disparity, which may cause visual fatigue of a user. On the other hand, the holography method provides both a binocular depth cue and a monocular depth cue. Accordingly, the holography method may display a three-dimensional image that does not cause substantial visual fatigue, and the holography method may provide a greater sense of a realistic image as compared to the stereoscopic method.
Despite the advantages of the holography method, there are many restrictions in displaying a three-dimensional image according to the holography method. Examples of such restrictions include an insufficient resolution of a spatial light modulator (SLM), a narrow viewing angle, existence of a direct current (DC) term and a conjugate image, an insufficient diffraction efficiency, a relatively large calculation capacity for a computer-generated hologram, and the like. From among these restrictions, an excessively narrow viewing angle is generally recognized as a main restricting factor. Holography generates a three-dimensional image by recording and reproducing a wavefront pattern. In order to display wavefronts of an object in a relatively wide angle, a pixel having a size corresponding to a size of wavelength is typically required. However, contemporary SLMs cannot make the wavefronts of an object be displayed at a wide angle, and contemporary SLMs only provide a narrow viewing angle to cover a single eye. Accordingly, other methods, such as a method using a plurality of SLMs or a method using a high speed SLM, have been attempted. However, these methods have typically required a complicated optical system and have generally been regarded as uneconomical.